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Set Up Reinjection

Reinjection is the process of queueing a message back to the customer’s server when it cannot be delivered due to conflicting SMTP errors after DATA. The reinjection host is often the same server as the outbound server, but this is not required.

Reinjection is necessary to avoid unexpected mail loss for a messages sent to multiple recipients. Fewer than 0.1% of all messages are reinjected. Before you can route mail through Outbound Services, the Administration Console checks that your reinjection host is configured to allow the email security service IP addresses to relay for external recipients.

You may have already set up your mail server and firewall to accept messages from the email security service, but reinjection requires further access. Your reinjection server must accept mail from the email security service and send it out again. This is called a private relay.

Configure your mail server and firewall to accept email only from the email security service. Your reinjection host needs to accept all email from the email security service’s outbound servers. From your server’s perspective, the email security service’s delivery servers should be considered a trusted server. Allow relaying only from the email security service’s IP range and other trusted relay servers.

If you have multiple mail servers, specify which server (or servers) will act as the reinjection host, and be sure that server can route mail back to the email security service.

Be careful when you set up a private relay. If you allow all IP addresses to pass mail through your server, your mail server will become an open relay. This leaves your mail server vulnerable to hijacking from malicious senders. Setting up a private relay is safer than an open relay, since malicious outsiders cannot use a private relay in the same way.

Setting up reinjection is different for every mail server type. For step-by-step instructions for setting up reinjection, see the appropriate chapter in this guide for your mail server.

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